The present invention relates to a fuel injection apparatus for an internal combustion engine.
In order to obtain optimum performance from a fuel injected internal combustion engine, the correct amount of fuel must be injected into the engine at the proper timing. Whereas in the past the emphasis has been on obtaining maximum production of mechanical power from internal combustion engines, due to the widespread pollution of the environment by automotive vehicles it has become increasingly necessary to concentrate on reducing the emission of pollutants from these vehicles.
Fuel injection pumps for Diesel engines are generally provided with governors which limit the engine speed to a predetermined maximum value. When the engine speed exceeds the maximum value the governor acts to sharply reduce the fuel injection volume and thereby reduce the engine speed below the maximum value. For the purpose of reducing pollutant emission, the fuel injection timing is retarded as the fuel injection volume is reduced. The retarded injection timing promotes more complete combustion due to elevated combustion temperature and thereby reduces the formation and emission of carbon monoxide and other pollutants which are products of incomplete combustion.
However, when the engine is operating under light load conditions, the amount of engine speed overshoot is greater than under heavy load conditions due to low inertia. Under such light load conditions, it is not desirable to retard the injection timing unconditionally since this results in the formation of nitrogen oxides. More specifically, due to the large engine speed overshoot the amount of fuel injected into the engine at high speed is extremely low. Although the resulting extremely high combustion temperature essentially eliminates the formation of carbon monoxide, it is so high that nitrogen oxides are formed. Thus, the desired effect of pollutant emission reduction is lost since unconditional retardation of injection timing merely results in the formation of a different pollutant.